The rat connective tissue mast cell was the first cell conclusively shown to store proteoglycans in an intracellular secretory granule compartment (Benditt et al., J. Histochem. Cytochem 4:419 (1956)). Rat connective tissue mast cells contain up to 25 pg/cell of an acidically charged .about.750 kDa (kilodalton) proteoglycan that possesses a very small peptide core to which approximately seven heparin glycosaminoglycans of 75-100 kDa are attached (Yurt et al., J. Biol. Chem. 252:518 (1977); Robinson et al., J. Biol. Chem. 253:6687 (1978); Metcalfe et al., J. Biol. Chem. 255:11753 (1980)). Because the peptide core of mature rat heparin proteoglycan consists almost entirely of equal amounts of serine and glycine (Robinson et al., J. Biol. Chem. 253:6687 (1978); Metcalfe et al., J. Biol. Chem. 255:11753 (1980)) and because heparin glycosyaminoglycan is O-glycosidically linked to serine at serine-glycine sequences within its peptide core (Lindahl et al., J. Biol. Chem. 240:2817 (1965)), it was first postulated by Robinson and coworkers (Robinson et al., J. Biol. Chem. 253:6687 (1978)) that the mature peptide core of this proteoglycan is predominantly an alternating sequence of serine and glycine.
It is now known that many cells of hematopoietic origin (including serosal mast cells, mucosal mast cells, basophils, natural killer cells, cytotoxic T lymphocytes, eosinophils, macrophages, and platelets) store a family of proteoglycans in a cytoplasmic granule compartment that is distinct from the plasma membrane-localized and extracellular matrix-localized families of proteoglycans (Stevens et al., Cur. Topics Microbiol. Immunol. 140:93-108 (1988)). These intracellular proteoglycans (known as "serine-glycine rich proteoglycans," "SG-PG," "secretory granule proteoglycan," or "serglycin proteoglycans") have five to seven highly sulfated glycosaminoglycans attached O-glycosidically to a common 18,600 to 16,700 M.sub.r peptide core possessing a protease-resistant glycosaminoglycan attachment region that is a repeat of serine and glycine amino acids (Yurt et al., J. Biol. Chem. 252:518-521 (1977); Robinson et al., J. Biol. Chem. 253:6687-6693 (1978); Razin et al., J. Biol. Chem. 257:7229-7236 (1982); Stevens et al., J. Biol. Chem. 260:14194-14200 (1985); Seldin et al., J. Biol. Chem. 260:11131-11139 (1985); Bourdon et al., Proc. Natl. Acad. Sci. USA 82:1321-1325 (1985); Bourdon et al., J. Biol. Chem. 261:12534-12537 (1986); Avraham et al., J. Biol. Chem. 263:7292-7296 (1988); Avraham et al., Proc. Natl. Acad. Sci. 86:3763-3767 (1989); Stevens et al., J. Biol. Chem. 263:7287-7291 (1988); Alliel et al., FEBS Lett. 236:123-126 (1988); Stellrecht et al., Nuc. Acids Res. 17:7523 (1989)). The peptide core of this family of proteoglycans has also been referred to by a variety of names, such as "secretory granule proteoglycan peptide core protein," but most recently has simply been called "serglycin." Thus, the gene encoding this peptide is the serglycin gene.
Serglycin proteoglycans (serglycin with attached glycosaminoglycans) are stored inside cells as a macromolecular complex bound to basically charged proteins. Because these proteoglycans are bound by ionic linkage in the secretory granules of mouse and rat mast cells to positively charged endopeptidases and exopeptidases that are enzymatically active at neutral pH, it has been assumed that the serglycin proteoglycans prevent intragranular autolysis of the proteases. The proteoglycan/protease macromolecular complexes remain intact when they are exocytosed from activated mast cells (Schwartz et al., J. Immunol. 126:2071-2078 (1981); Serafin et al., J. Biol. Chem. 261:15017-15021 (1986); Serafin et al., J. Immunol. 139:3771-3776 (1987); Le Trong et al., Proc. Natl. Acad. Sci. USA 84:364-367 (1987)), presumably attenuating diffusion of the proteases from inflammatory sites and facilitating concerted proteolysis of protein substrates.
cDNAs that encode serglycin have been isolated from rat (Bourdon et al., Proc. Natl. Acad. Sci. USA 82:1321-1325 (1985); Bourdon et al., J. Biol. Chem. 261:12534-12537 (1986); Avraham et al., J. Biol. Chem. 263:7292-7296 (1988)), mouse (Avraham et al., Proc. Natl. Acad. Sci. 86:3763-3767 (1989)), and human (Stevens et al., J. Biol. Chem. 263:7287-7291 (1988); Alliel et al., FEBS Lett. 236:123-126 (1988); Stellrecht et al., Nuc. Acids Res. 17:7523 (1989)) cDNA libraries. These cDNAs encode 1.0-, 1.0-, and 1.3-kb transcripts in the mouse, rat, and human, respectively. The mouse serglycin gene resides on chromosome 10, is approximately 15 kb in size, and consists of three exons (Avraham et al., Proc. Natl. Acad. Sci. 86:3763-3767 (1989)).
Bourdon and coworkers (Bourdon et al., Proc. Natl. Acad. Sci. USA 82:1321 (1985); Bourdon et al., J. Biol. Chem. 261:12534 (1986)) isolated and characterized a cDNA from a rat yolk sac tumor cell that encoded an unusual 18.6 kDa proteoglycan peptide core with a 49 amino acid glycosaminoglycan attachment region of alternating serine and glycine. Because of the preponderance of these two amino acids, it was proposed that the peptide core of this proteoglycan (designated serglycin) was related to the peptide core of rat mast cell-derived heparin proteoglycan. Numerous molecular biology studies have been carried out on the cDNAs and genes that encode mouse, rat, and human serglycin. Using a 3' gene-specific fragment of a rat serglycin cDNA (Avraham et al., J. Biol. Chem. 263:7292 (1988)), it was demonstrated that this gene is expressed at relatively high levels in a variety of mouse and rat mast cells irrespective of what type of glycosaminoglycan is polymerized onto the peptide core (Tantravahi et al., Proc. Natl. Acad. Sci. USA 83:9207 (1986)). This gene is also expressed in many other hematopoietic cells that possess secretory granules (Tantravahi et al., Proc. Natl. Acad. Sci. USA 83:9207 (1986); Stevens et al., J. Immunol. 139:863 (1987); Stevens et al., J. Biol. Chem. 263:7287 (1988); Rothenberg, M. E., Pomerantz, J. L., Owen, W. F., Avraham, S., Soberman et al., J. Biol. Chem. 263:13901 (1988); Stellrecht et al., Nucleic Acids Res. 17:7523 (1989); Perin et al., Biochem. J. 255:10017-1013 (1988); MacDermott et al., J. Exp. Med. 162:1771 (1985); Nicodemus et al., J. Biol. Chem. 265:5889 (1990)) and it appears that the same peptide core is used in all of these cell types. The selection of the type of glycosaminoglycan that will be synthesized onto this peptide core therefore appears to be a cell-specific event that is not exclusively dependent on the translated peptide core.
Although serglycin is specifically expressed in hematopoietic cells, no tissue specific hematopoietic cell transcriptional regulatory elements have yet been identified. A need exists for such elements as they would allow, for the first time, the regulated induction or expression of recombinant genes in hematopoietic cells, especially in hematopoietic cell culture systems.